1. Field of the Invention
The present invention relates in general to an electric power steering system and more particularly to an electric power steering system capable of informing a driver of potential danger by providing control by way of safety precaution before a vehicle enters a dangerous situation.
2. Description of the Prior Art
As a prior art system related to the present invention, a system for warning of a vehicle accidentally drifting out of the traffic lane is disclosed in Japanese Unexamined Patent Publication No.6-76200 (1994). This prior art system is mainly directed to a system for warning a driver when the vehicle starts drifting out of the lane as a result of his falling asleep. This system keeps watch on the traffic lane (a line on a road) using a television camera and gives a warning to the driver when the vehicle starts drifting out of the lane. To give the warning, a vibration actuator incorporated in the steering wheel directly vibrates a spoke portion of the steering wheel.
Dangerous situations which are expected to occur while the vehicle is moving include not only cases where the vehicle is not steered because the driver has fallen asleep behind the wheel, but also those where the driver is steering the wheel.
Referring to FIG. 1, suppose that Vehicle C1 in the left lane and Vehicle C2 in the right lane are moving in the same direction on a divided road R with two lanes each way; Vehicle C1 is running somewhat ahead relative to Vehicle C2, and Vehicle C2 is approaching Vehicle C1 from the right rear and is moving at a faster speed than Vehicle C1.
When the vehicles so positioned are moving, if the driver of Vehicle C1 is not aware of the approach of Vehicle C2 from the right rear and tries to change lanes, as shown by the broken line in the figure, a dangerous situation may occur which could cause a collision.
Such danger does not stem from the fact that the driver has, for example, fallen asleep behind the wheel and has not actively steered the vehicle, as is the case described in the prior art system, but rather results from the fact that the driver carelessly has failed to check his rear to make sure that he may safely change lanes and has turned the steering wheel.
The prior art system does not fully assure the prevention of occurrence of dangerous situations caused by such carelessness of the driver. It is extremely dangerous to cause vibration in the steering wheel in response to the detection of the white dividing line by the television camera when the driver is actively turning the steering wheel to change lanes.